Vehicle Mounted Steerable Antenna Array for NATO band III Applications

Abstract

This thesis investigates a compact 2×2 phased array intended for vehicle roof-mounted applications across NATO Band III (1350–2400 MHz). The work addresses design and experimental validation of phase-only azimuth null steering under tight inter-element spacing, considering practical constraints of a finite ground plane and laboratory measurement uncertainty. Array geometry and spacing were developed through simulation-guided parametric studies and array-theory considerations. Two single-element prototypes – copper sheet and copper tape – were fabricated and compared, with the latter selected for array implementation based on geometric consistency and simplified manufacturing. Validation was performed in an anechoic chamber and in a spherical near-field system. The steering method employs fixed amplitudes with per-port phase optimisation to realise commanded azimuth nulls. Embedded element measurements (one port excited, others terminated) were used to characterise radiation in the presence of mutual coupling and to extract frequency-dependent realised gains. A commercial antenna was used as a reference mostly for gain as the antenna is not capable of beam or null steering.

Across the band and steering directions considered, the array produced repeatable phase-only nulls with front-to-back ratios in the range of 10–30 dB, subject to frequency and geometry. Full-wave simulation revealed that uncoupled array factor predictions overestimate achievable null depths by over 50 dB at this spacing, confirming the necessity of embedded-element characterisation. The compact spacing produced no grating lobes across the operating band, and diagonal steering directions (225°, 315°) consistently achieved greater suppression than perpendicular directions (180°, 270°) due to the larger effective element spacing along the diagonal.

The achieved front-to-back ratios represent a practical baseline for interference suppression, though several factors limit performance. The 2×2 aperture restricts degrees of freedom to three independent nulls maximum; larger apertures would enable deeper and multiple simultaneous nulls. Phase-only control produces frequency-dependent beam pointing that requires per-frequency optimisation; true time delay would eliminate this limitation at increased hardware complexity. Finite ground plane dimensions and facility-specific measurement effects introduced several decibels of variation between facilities. Targeted improvements include coupling-aware weight synthesis to improve null depth, amplitude control for additional optimisation flexibility, and on-vehicle validation to assess platform effects under operational conditions.